Welding has long been used in manufacturing, construction and related fields as a method of creating, strengthening and repairing connections between and among components, structural or decorative panels, beams, etc. The widespread use and many variant applications of welding technology have led to the development of a wide variety of welding strategies and types of equipment over the years. In general terms, welding, in contrast to certain other joining techniques, involves melting adjacent areas to be joined, then allowing the resultant molten pool of material to re-solidify and thereby form a metallurgical bond between the areas.
One common type of welding is known as electrical arc welding, which typically utilizes a welding “torch” having one or more electrical wires from which an electrical arc is generated, passing between the tips of the wires and regions of the workpiece(s) sought to be joined. The electrical arc generates intense heat which melts portions of the electrical wire and the workpiece, forming a molten material pool which can re-solidify to form the desired joint.
One attempt at improving the efficiency and reliability of electrical arc welding is through the use of multiple welding wires in a single welding torch. Multiple welding wires extending from a welding torch end or nozzle can in some cases allow a welding technician or robot to weld adjacent sides or edges of a joint in a single pass, rather than requiring separate passes to weld material at each side or “root” of the joint. The multiple welding wires also tend to generate a relatively larger molten pool of material and higher welding deposition rate as compared to the use of a single welding wire.
While the use of multiple welding wires in a single welding torch, often termed a “tandem” welding torch, has been relatively successful, there is always room for improvement. In particular, it can be difficult to position the welding wire tips in optimum locations for welding in certain types of joints. In the case of joints between relatively thick pieces of material, it is often necessary to prepare the joint prior to welding such that the welding wire tips can be maneuvered to positions relatively close to the roots. Positioning the welding wire tips at an optimum position close to the roots has been shown to increase productivity and weld quality, as well as requiring relatively less energy to weld given the relatively shorter necessary arc length. While various strategies are known which are directed to enabling better maneuverability of welding wires toward optimum welding positions, engineers have continued to struggle to develop robust tandem welding torch designs without sacrificing weld quality in production.
One common joint type that tends to require relatively onerous preparation prior to welding is known as a butt joint. Butt joints typically include adjacent peripheral edges of workpiece members positioned generally in parallel. In other words, in a typical butt joint the peripheral edges of the workpieces are generally aligned with one another edge to edge. The workpiece members may be panels, beams, pipes, etc., and are typically separated by a gap to allow the wires of the welding torch to be positioned as close to the joint roots as practicable. A backing plate may be positioned to extend across the gap such that a channel exists, defined by the backing plate and the facing edges of the work piece members. During welding, the wires are moved within the channel.
It has long been considered challenging to optimally maneuver the welding wires along the roots of a butt joint with a traditional welding torch to weld a satisfactory joint. Aberrations in the uniformity of a welded joint can lead to cracks, that may begin from voids adjacent roots that never melted during the first pass of the welding procedure. Poorly welded joints can ultimately require expensive and time-consuming repairs. In an attempt to improve welded joint integrity, adjacent workpiece members to be joined via welding are typically either spaced relatively far apart, still tending to lessen the end integrity of the joint, or the workpieces are specially prepared, such as by including a torch access bevel on the tops of aligned workpiece edges, prior to welding, to facilitate positioning and maneuvering of the welding wires.
Where dual wire welding torches are used, the electrical arcs can generate magnetic fields which cause the welding wires to move out of a desired position within the joint, resulting in sub-optimal or irregular fusion of the backing plate and workpiece members and reduced overall soundness of the joint. This phenomenon is particularly acute where relatively longer welding wires are used. While certain welding torches address these concerns to some extent, for example via spinning the welding wires while feeding or via magnetically and/or mechanically oscillating the electrical arcs to assist in orienting the welding wires as desired, such torches tend to be rather unwieldy and difficult to precisely maneuver, or are fragile and ill-suited to production environments.
As alluded to above, special preparations are sometimes made prior to welding in an attempt to improve joint integrity and production efficiency. To this end, the workpiece members of a butt joint are often beveled via machining such that they have a cross section giving sufficient room for the welding torch and its associated welding wires to be maneuvered to the roots of the joint. It will be readily apparent that a separate machining step prior to welding a butt joint, or for that matter, any other joint, is time consuming, expensive, and wastes material.
U.S. Pat. No. 6,172,333 to Stava is directed to one type of welding apparatus configured with dual welding wires for welding a gap between adjacent pipe sections. In Stava, the respective welding wires are moved in union on opposite sides of the gap. As in other known designs, in Stava the workpiece sections defining the gap are beveled to permit desired positioning of the welding wires. Stava further proposes an adjustment feature for adjusting the spacing of the wires, purportedly to accommodate different sized gaps. While Stava may have certain advantages over other known designs, the strategy still requires painstaking joint preparation prior to welding, for at least certain types of joints.